Polymide resins superior in heat resistance and outstanding in electrical properties, mechanical properties, etc. have been used in the surface-protecting film and interlayer dielectric of a semiconductor chip. Meanwhile, in recent years, semiconductor chips have become more highly integrated and larger, resin-encapsulated packages have become thinner and smaller, and surface mounting by reflow soldering has come to be adopted; for these and other reasons, significant improvements in heat cycle resistance, thermal shock resistance, etc. have come to be required for polyimide resins, and a polymide resin of higher performance has become necessary.
Meanwhile, attention has recently been paid to a technique of allowing a polyimide resin itself to have photosensitivity. Photosensitive polyimide resins include, for example, one represented by the following formula (3). 
Use of the above resin enables simplification of a part of pattern formation step and shortening of the step but requires, in development, a solvent such as N-methyl-2-pyrrolidone or the like, posing a problem in safety and handling. Hence, positive photosensitive resins which can be developed with an aqueous alkali solution, have been developed recently. In, for example, JP-B-1-46862 there is disclosed a positive photosensitive resin constituted by a polybenzoxazole precursor and a diazoquinone compound. This resin has high heat resistance, excellent electrical properties and fine processability, and is usable as a wafer-coating resin and further may be used as a resin for interlayer insulation. As to the mechanism of development of this positive photosensitive resin, the diazoquinone compound which is insoluble in aqueous alkali solution when unexposed to a light, gives rise to a chemical change when exposed to a light and becomes soluble in aqueous alkali solution. Owing to this difference in solubility in aqueous alkali solution between exposed portion and unexposed portion, it is possible to form a coating pattern constituted by the unexposed portion alone.
In recent years, photosensitive resins have been strongly required to have, in particular, a high sensitivity. The reason is that, with a low sensitivity, the exposure time per one wafer is long, resulting in a low through-put. In order for a photosensitive resin to have a high sensitivity, it is considered to, for example, make smaller the molecular weight of a polybenzoxazole as a base resin. With this approach alone, however, film thinning of unexposed portion during development is large, making it impossible to obtain a desired film thickness and, moreover, giving a pattern of inferior shape. Further, the cured film formed by thermal dehydration and ring closure is significantly low in mechanical properties. For these reasons, it has been desired to develop a photosensitive resin satisfying the above properties and yet having a high sensitivity.
In addition, in recent years, wafers, in particular, have become larger and wafers of 300 mm have come to be used. With a large wafer, however, warpage arises owing to a difference in linear expansion coefficient between silicon wafer and photosensitive resin and there are problems, for example, cracking of wafer in back side grinding step for wafer thinning. Therefore, it has been desired to develop a photosensitive resin of low stress having a linear expansion coefficient close to that of silicon wafer.